1. Technical Field
The invention concerns a production process for a semiconductor component having a silicon-bearing layer, a praseodymium oxide layer and a mixed oxide layer which is arranged between the silicon-bearing layer and the praseodymium oxide layer and which contains silicon, praseodymium and oxygen. The invention further concerns semiconductor components produced by way of the process and electronic devices with semiconductor components of that kind.
2. Discussion of Related Art
Pr2O3 layers on Si(001) substrates, because of their comparatively high dielectric constants (k≈30), are particularly suitable for replacing the traditional gate-dielectric material SiO2 in sub-0.1 μm CMOS technology. It is however generally assumed that an ultra-thin SiO2 layer is necessary between the Si substrate and an alternative dielectric material in order to match bondings and charges to each other and to reduce mechanical stresses and in that way to achieve a high level of charge carrier mobility.
As the following consideration shows, such a thin SiO2 intermediate layer reduces the dielectric effectiveness of the substitute material. If we assume that the thickness thigh.k of the alternative dielectric is to afford the same capacitance as an SiO2 layer of the equivalent thickness teq, that gives:thigh-k=(khigh-k/kSiO2)teq,  (1)wherein kSiO2 is the dielectric constant of the SiO2. As the SiO2 intermediate layer represents a second capacitance CSiO2 connected in series with the alternative dielectric, the resulting capacitance can be calculated as follow:1/Cres=1/Chigh-k+1/CSiO2,  (2)wherein Chigh-k is the capacitance of the dielectric layer. Using (1), that then gives the following for the equivalent thickness of the layer system tseq, comprising a thin SiO2 layer tSiO2 and the dielectric layer thigh-k,tseq=tSiO2+(kSiO2/khigh-k)thigh-k,  (3)
It follows directly from (3) that the minimum attainable equivalent oxide thickness tseq can never be less than the thickness tSiO2 of the SiO2 layer. Consequently, in the series connection of two capacitances with very different dielectric constants the material with the lower dielectric constant—in general the SiO2—will limit the maximum possible capacitance of the layer stack.
While a very high capacitance in respect of the layer, in the case of extremely slight leakage currents, is essential for use of the material in dynamic RAMs (DRAMs), a very high interface quality and charge carrier mobility in the channel are crucial for use of the material in MOSFETs.
There is therefore a need for alternative materials for forming an intermediate layer between the silicon-bearing layer and the praseodymium oxide layer, wherein that intermediate layer both should have a greater dielectric constant than SiO2 and also should have adequate chemical and thermal stability in relation to the working processes which are currently employed in semiconductor technology.
One approach for establishing semiconductor components with a sufficiently high capacitance and charge carrier mobility even when particularly small dimensions are involved provides a mixed oxide layer which is arranged between the silicon-bearing layer and the praseodymium oxide layer and which contains silicon, praseodymium and oxygen. That mixed oxide layer is necessary to achieve adaptation of crystal structure and charge. A suitable mixed oxide layer is chemically and thermally stable, it involves a low defect density and it does not contain any silicide phases.
It will be noted however that it has been found that, in the direct growth of the mixed oxide layers on the silicon-bearing semiconductor layer, depending on the process conditions involved, active or passive oxidation of the silicon surface takes place. In particular active oxidation which dominates at temperatures above 600° C. and with low oxygen partial pressures results in roughening of the silicon surface as a consequence of SiOx desorption and thus results in a poorer quality both in respect of the interface between the mixed oxide layer and the silicon-bearing layer and also in respect of the mixed oxide layer.